1. Field of the Invention
The present invention relates to a photocurable adhesive composition, and particularly to a photocurable adhesive composition for use in displays and touch panels.
2. Description of the Prior Art
With the fast growth of the information industry, electronic products such as mobile phones, personal digital assistants and notebooks have become daily necessities in the life of modern-day individuals. A display is an indispensable interface that allows the human-machine communication in these electronic products to take place. How to provide products that are lighter and thinner and have better visual effects has always been one of the main purposes behind the developments within the industry. Recently, touch panel has been integrated with display for use in various electronic products; users can touch the panel and conduct each of the operations such that a more convenient and humanized operation mode can be provided.
As shown in FIG. 1, the exterior portion of a normal touch panel includes cover lens 11 made of a polyester film or glass for strengthening and protecting the touch panel, and an adhesive layer 12 for adhering the cover lens 11 to an ITO film or ITO glass 13.
Adhesives have extensive applications, among which optically-transparent adhesives are widely used in displays and touch panels to provide adhesion effects. Typical applications of such adhesives include, for example, adhering a touch panel onto a display and adhering an ITO film or ITO glass of a touch panel to an exterior film or glass. To prevent affecting the visual effects, such adhesives should exhibit proper optical properties such as proper light transmittance and refractive index.
When light travels through different mediums, reflection occurs due to the difference in refractive indexes, thereby affecting light's extraction efficiency. Optical devices, such as thin film and glass, usually have a relatively high refractive index. For example, the refractive index of glass is about 1.52. Nevertheless, a common optically-transparent adhesive, such as acrylate adhesive, has a refractive index of about 1.4 to 1.45, which cannot meet the demand of the industry. Therefore, in order to reduce optical devices' reflection of light and to increase light transmittance, an optically-transparent adhesive with a high refractive index is needed in the industry.
Up to now, the optically-transparent adhesives used in the industry include optical adhesive tape, liquid optically clear adhesive and other similar products. When using optical adhesive tape, it needed to be kept smooth during the adhering process; otherwise, bubbles or wrinkles could generate. In addition, optical adhesive tapes have their disadvantages, such as the complexity of the adhering steps, the lack of reworkability and the necessity for a sufficient thickness. In order to improve the yield of the process, to simplify the steps involved in the process and to meet the requirements for producing a thinner and lighter product, liquid optically clear adhesives have been attracting more attention.
In general, liquid optically clear adhesives often encounter certain disadvantages, such as poor light transmittance and low refractive index, and the flow properties thereof must be properly adjusted so as to avoid the problem of an overflow. In some circumstances, for example, when liquid optically clear adhesives are used in touch panels, they must have the appropriate softness so as to provide excellent cushioning properties and to avoid undesirable visual effects such as water ripple appearing in the touch panels due to stress.
Therefore, the present invention provides a photocurable adhesive composition with a high refractive index. The photocurable adhesive composition of the present invention has appropriate flowability and softness, is easy to be coated and adhered, and can improve the visually aesthetic appearance of screens, thereby effectively resolving the problems encountered in the prior art.